The invention relates to a pressure medium unit, having a housing which is made from plastic, is manufactured by way of injection molding, and in the housing wall of which at least one connector socket with a through opening is fastened, through which through opening a feed and/or discharge of pressure medium into or out of the interior of the housing takes place, and by a method for producing the same.
The field of use of the invention extends, in particular, to pressure medium units which are operated by way of compressed air as pressure medium, such as multi-way valves, brake cylinders and the like. Units of this type usually have connector sockets for connecting pressure medium lines or pressure medium pipes made from plastic. In order to mount the connector socket, the housing of the pressure medium unit is provided with a fitting blind bore, the diameter of which is adapted to the external diameter of the connector socket.
A pressure medium assembly of the generic type is known, for example, from DE 30 26 596 A1. In DE 30 26 596 A1, the connector socket is pressed in a through opening of a cover, which is injection molded from plastic, of a diaphragm cylinder which is configured as a pneumatic brake cylinder.
Housings of pressure medium units, into which connector sockets of this type are pressed, are often injection molded from high strength, for example glass fiber reinforced, plastics for reasons of strength. When a connector socket is pressed into a corresponding blind bore of an injection molded housing of this type, the problem occurs that pressing stresses are introduced into the housing, which pressing stresses can lead to crack formations or to the fracture of the housing in the case of the predominantly low wall thicknesses of the housings. This is because high strength plastics of this type have only a low elastic capability.
EP 1 371 856 A2 discloses a pressure medium unit, on the housing of which a connector socket is introduced into a corresponding blind bore. Here, the fastening takes place not by way of being pressed-in, but rather via at least one recess which is provided in the wall region of the blind bore and interacts in the manner of a positively locking snap action connection with at least one hook-like molded projection on the connector socket which is adjusted to the blind bore in a pressure-tight manner. It is a disadvantage here, however, that the fastening of the connector socket takes place in this solution merely via two apertures in the housing which lie opposite one another as positively locking connecting points.
In contrast, the invention is based on the object of fastening a connector socket in the housing of a pressure medium unit in such a way that, firstly, a high retaining force of the connector socket in the housing wall is ensured and, secondly, critical stresses in the housing of the pressure medium unit are avoided.
According to the invention, said object is achieved by way of a pressure medium unit, and a method for assembling it, in accordance with embodiments of the invention.
In the pressure medium unit according to the invention and/or in the method for producing it, the connector socket, with the exception of the through opening, is injection molded at least partially into the housing wall during the injection molding of the housing. In other words, the housing is injection molded from plastic and, at the same time, the connector socket is injection molded at least partially into the housing wall in a single work step as early as during the production of the housing and within the context of the injection molding operation, at least the through opening of the connector socket not being covered by or being exposed by the injection molding material, in order to ensure an unobstructed and intended feed and discharge of pressure medium through the through opening.
The production method, from which the invention proceeds, comprises at least the step of injection molding the housing from plastic in an injection molding die. According to the invention, the at least one connector socket is then positioned in the injection molding die at the point which is provided for it and, with the exception of the through opening, is injection molded at least partially into the housing wall during the subsequent injection molding of the housing.
At least partial injection molding is understood to mean, in particular, injection molding, in the case of which at least part of the axial extent of the connector socket is injection molded into the housing wall as viewed in the direction of its center axis. Here, for example, part of the connector socket can still protrude, in particular, out of the outer face of the housing wall. As an alternative, the connector socket can be injection molded along its entire axial extent into the housing wall. It is merely decisive that no plastic is injection molded into the through opening, in order that the latter can still function as intended. Therefore, an outer circumferential face of the connector socket, with the exception of the through opening, is injection molded partially or completely in the housing wall.
As a result of the abovementioned measures, an integrally joined connection occurs between the radially outer circumferential face of the connector socket and the housing wall. This integrally joined connection ensures a high retaining force of the connector socket in the housing wall, without stresses which damage the housing wall, for instance, being produced as a result.
The connector socket is particularly preferably configured for releasably fastening a connector stub of a hose or pipe line, which connector stub conducts the pressure medium. To this end, the connector socket can be configured, in particular, in the manner of a push-in fitting for releasably fastening the connector stub which conducts the pressure medium. Threaded, plug-in or latching connections are contemplated here.
In order to seal the releasable connector stub/connector socket connection, at least one seal element can be arranged between a radially outwardly protruding collar of the connector stub and an outer face of the housing wall or an end face of the connector socket. Here, the seal element which is formed, for example, by way of an elastic sealing ring is held between the collar and the outer face of the housing wall or the end face with axial prestress, which has a favorable effect on the sealing action.
According to one particularly preferable embodiment, the connector socket has a sleeve part and a collar part which protrudes radially outwardly away from the sleeve part. At least the collar part preferably is molded completely into the housing wall by way of the injection molding operation. The collar part then ensures, in particular, satisfactory anchoring of the connector socket in the housing wall, even preferably with regard to loads perpendicularly with respect to the plane of the collar part as occur, for example, during the axial insertion or screwing of a connector stub into the connector socket.
According to one further embodiment, for the purpose of an anti-rotation safeguard of the connector socket with respect to the housing wall, the collar part can have a radially outer circumferential face which differs from a rotationally symmetrical face. This can be realized, for example, by virtue of the fact that the collar part has a radially outer circumferential face which is polygonal as viewed in cross section, for example a hexagonal cross section. As an alternative or in addition, the anti-rotation safeguard might also be realized by virtue of the fact that the collar part has at least one transversely extending through opening which is penetrated by the material of the housing wall.
An anti-rotation safeguard is advantageous, in particular, when the connector socket has an internal thread in its through opening, into which internal thread an external thread of a connector stub is then screwed, the connector socket being subjected to torsional loading.
As described above, the connector socket can be injection molded along its entire axial extent into the housing wall. The sleeve part then extends substantially from an inner face as far as an outer face of the housing wall.
According to a further embodiment or in addition to the above-described embodiment, for the purpose of an anti-rotation safeguard of the connector socket with respect to the housing wall, a radially outer circumferential face of the connector socket can have a shape which differs from a rotationally symmetrical face as viewed in cross section. There is then no collar part, and the sleeve part or the radially outer circumferential face has, for example, a polygonal cross section.
In order to ensure high wear resistance, high strength and stiffness in the context of high functional reliability with regard to repeated connecting and release operations of the connector stub in relation to the connector socket, the connector socket preferably consists of at least one metal or of a metal alloy.
The pressure medium unit is particularly preferably formed as a pneumatic brake cylinder, and the through opening of the connector socket then serves to fill and/or vent a brake chamber in the interior of the brake cylinder.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.